Eli Greene

Thanks for all the help, Yea the reason that I feel that it has something to do with IMC is that it only seems to happen after spending >20minutes in the clouds. I've never seen it happen outside of the clouds or when in the clouds for a short while. Obviously the alternator's don't understand whether IMC exists around them, but I'm wiling to bet that the clouds are getting the alternator wet. When it first happened, I was in the clouds, no rain but quite a bit of water/water droplets. Second time it happened we were in pretty heavy rain. Third time it happened no rain, just in the clouds. All three times I had been in the clouds for at least 20 minutes, although in the first 2 cases it was about an hour before anything happened. This leads me to believe that clouds/water from the clouds getting onto the airplane and into some connections could be causing the issue... From what little I understand, I guess the water may be causing an overvoltage for some reason, leading to an overvoltage trip. This would be consistent with being able to reset the alternator, and would be consistent with water getting in. I'm guessing that this all points towards a new voltage regulator, but I will check over the connections obviously before immediately going that route. -Eli

I have a 1975 M20F and have been having an intermittent issue with my alternator in IMC. Back in July of last year, I went on about a 3 hour flight through IMC. About 2 hours in, while in IMC, the alternator died. We had a low voltage warning light, negative amps draw, and voltage of 11.9 volts. Circuit breakers were ok, we unplugged/turned off all non-essential equipment, and continued the flight. After a few minutes, we decided to cycle the master switch, and this worked. The alternator returned and we landed without event. The mechanic on the ground couldn’t find any issues, and our flight home was set to be VFR conditions, so we continued home with no problems. We had the alternator inspected at our home airport, and no issues were found. I don’t fly through large amounts of IMC(being from Colorado it’s normally icy, so I didn’t see the issue arise or fly long IFR flights much after that incident. In October, we got the engine overhauled, resetting most of our stuff firewall forward. I felt that this would likely also have alleviated our issues with the alternator. However, now I have experienced the issue again. First, yesterday we lost the alternator in IMC intermittently for maybe 20 seconds. Today, we lost the alternator for about 10 minutes at the end of our flight. After getting on the ground, I cycled the master switch and it reacted exactly the same as the first time, with the alternator coming right back. I have heard of issues with early model Mooneys ingesting too much water and having that hurt the alternator. I have the lower cowl enclosure which makes me believe it would be less of an issue for me but I’m not sure. Either way I’ve had the same issue 2-3 times through one overhaul. Does anybody know what this issue could be?